Protection from chlordecone-amplified carbon tetrachloride toxicity by cyanidanol: Regeneration studies

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Previous work has shown that chlordecone (CD)-amplified CCl 4 hepatotoxicity and lethality can be mitigated by pretreatment with cyanidanol. These studies also revealed that stimulated hepatocellular regeneration might play an important role in the cyanidanol protection of CD-amplified CCl 4 toxicity. The present studies conducted over a time course of 0 to 120 hr after CCl 4 challenge describe sequential changes in hepatic [ 3H]thymidine incorporation into hepatocellular nuclear DNA, polyamines and related enzymes, and histomorphometry of liver sections from variously treated rats. Male Sprague-Dawley rats (125–150 g) were maintained on a control diet or on a diet contaminated with CD (10 ppm) for 15 days and/or pretreated with cyanidanol (250 mg/kg, ip) at 48, 24, and 2 hr befor a single ip injection of either a standard protocol dose (100 μl/kg) or a low dose (50 μl/kg, L) of CCl 4 on Day 16 of the dietary protocol. Cyanidanol pretreatment significantly stimulated the hepatic [ 3H]thymidine incorporation into hepatocellular nuclear DNA of control rats irrespective of CD pretreatment. Similarly, polyamine metabolism was altered favorably for cell division, although mitotic index (metaphase) was not increased. Cyanidanol-stimulated [ 3H]thymidine incorporation was highly suppressed in rats receiving the CD + CCl 4 standard dose combination treatment up to 36 hr, but after this time point a marked increase was observed. Hepatocellular regeneration, quantified histomorphometrically as volume density of cells in metaphase, was progressively increased in rats protected from CD + CCl 4 interaction by cyanidanol, starting at 36 hr and lasting until 72 hr. Favorably altered polyamine metabolism was evident from the stimulated ornithine decarboxylase, as well as from the stimulated interconversion of the higher polyamines to maintain increased concentration of putrescine. Challenge by the same dose of CCl 4 (100 μl/kg) to CD-pretreated rats not protected by cyanidanol failed to cause any increase in [ 3H]thymidine incorporation up to 36 hr and resulted in animal death starting at 36 hr. In the surviving rats, [ 3H]thymidine incorporation at 48 hr was increased, but was less than 50% of the increase observed in the cyanidanol group. In these rats, attenuation in the stimulation of cell division and insufficiently increaed putrescine levels were observed, which are consistent with the inadequate level of hepatocellular regeneration. With rats receiving CD + CCl 4(L) combination, the [ 3H]thymidine incorporation at 48 hr was less than 50% of the increase of cyanidanol-protected rats. Cyanidanol pretreatment to the CD + CCl 4 group of rats prevented the decrease in the hepatic DNA levels. CCl 4 challenge to control rats did not show any discernible alterations in the hepatic DNA levels. However, CCl 4 administration to CD-pretreated rats caused a significant and progressive decrease in hepatic DNA starting at 6 hr until animal death. Similarly, CD + CCl 4(L) rats showed a significant decrease in hepatic DNA at 24 and 48 hr, whereas, in the surviving rats a recovery in DNA levels was observed. These results suggest that the major event in the cyanidanol protection of CD-amplified CCl 4 toxicity is the stimulation of hepatocellular regeneration targeted for tissue repair.